1. Field of the Invention
This invention relates in general to an apparatus and method for preparing multiphase gypsum and particularly a wall plaster which has an exactly defined composition.
2. Description of the Prior Art
When multiphase gypsum is burned in a carrier gas installation particularly a cyclone type burning installation which has at least two stages the heating gas flows through the burning stages or cyclones consecutively but only a part of the raw material which has to be converted, for example into an anhydrite (high temperature burnt gypsum) passes through the stages consecutively while the part of the raw material to be converted into hemihydrate (low temperature burnt gypsum) is removed from the upper stage. Thereafter the high temperature burnt portion and the low temperature burnt portion are cooled in a common cooling equipment and mixed with each other.
Since the entire volume of heating gases flows through both the treatment stages and therefore in the upper stage or pre-burning stage all of the raw material is heated in the same manner, there is no possibility to further individually influence the low temperature burnt gypsum which is removed from the upper stage. This is disadvantageous because in the manufacture of multiphase gypsum such as wall plaster which has a quite definite composition of phases it would be desirable to control the calcination process so as to obtain a final product which is free from dihydrate and comprises only a minimum of the mostly undesirable anhydrite III phase.